Apparatus for cleaning stack gas and using same for generation of electric power

ABSTRACT

Stack gas is first passed through a coarse-particle separator and then a prescrubbing tower. Then this gas, which is under pressure, is passed through a pair of differential-pressure (annular-gap) washers. The output side of one of the washers is connected directly to a droplet separator at the output of the system. The outlet of the other washer is connected through a turbine driving an electric generator and having its output side in turn connected to the droplet separator. The control body of at least the washer which is connected directly to the droplet separator is adjustable so as to maintain a constant backpressure in the system at the blast furnace from which the stack gas comes. The washer connected to the turbine is set up to pass at least four times as much of the gas as the other washers so that most of the gas passes through the turbine, undergoing a pressure drop that is transformed into the work of driving the turbine and generates electricity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 692,731 filedJune 4, 1976 (U.S. Pat. No. 4,055,331) as a continuation-in-part of Ser.No. 520,920 filed Nov. 4, 1974 (U.S. Pat. No. 4,007,025) and is relatedto commonly assigned and then pending application Ser. No. 345,762 filedMarch 28, 1973 (U.S. Pat. No. 3,854,908 issued Dec. 17, 1974) as acontinuation-in-part of application Ser. No. 235,208 filed Mar. 15, 1972(U.S. Pat. No. 3,844,744) citing application Ser. No. 188,557 filed Oct.12, 1971 (U.S. Pat. No. 3,726,065).

FIELD OF THE INVENTION

The present invention relates to apparatus for treating pressurizedstack gas. More particularly this invention concerns the treatment ofsuch gases issuing from high-pressure blast furnaces and the like.

BACKGROUND OF THE INVENTION

Hot stack gases which issue from a blast furnace or the like at apressure of several atmospheres are usually passed through a cleaning orpurifying device which first separates out the larger particles carriedby the gas and then subjects the gas to a scrubbing operation whichremoves many of the water-soluble gas components and removes additionalparticles from the gas stream.

The above-cited earlier works describe so called Venturi ordifferential-pressure (annular-gap) washers which comprise a tube havinga narrow waist in which is received a body that is displaceable withinthis tube so as to define a variable gap therewith. A sprayer isprovided in the upstream end of the tube so that the turbulence andpressure drop in the tube will thoroughly scrub the remaining particlesfrom the gas.

Such differential-pressure (annular-gap) washers are used to maintain aconstant backpressure in the blast furnace. A constant backpressure isnecessary for proper functioning of the furnace and can readily bemaintained by the washers. At the same time such devices serve to dropthe pressure so that the cleaned stack gases can be used in regeneratorsfor heating up the charge or the air that goes into the furnace. As arule a plurality of such annular-gap washers are used with all of theirinsert bodies coupled together so as to permit adjustment of thepressure drop across them to maintain the pressure in the blast furnaceconstant.

Such systems are relatively effective. However they have the principaldisadvantage that they waste a considerable amount of energy present inthe hot pressurized stack gas. A significant amount of energy availableto do work is wasted as the gases pass through the washers and expand.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved apparatus for cleaning stack gas.

Another object of this invention is to provide a stack-gas cleaningapparatus which recovers at least a portion of the energy present in thestack gas.

Yet another object is the provision of an apparatus which allows thepressure in the blast furnace to be maintained constant for mostefficient blast-furnace operation.

SUMMARY OF THE INVENTION

These objects are attained according to the present invention in anapparatus for cleaning stack gas from a high-pressure blast furnace orthe like which uses a pair of differential-pressure (annular-gap)washers connected either in parallel or in series with one another inthe gas path from the prescrubber. The output side of one of thesewashers is connected directly to the discharge end of the system and theoutput side of the other washer is connected through a turbine to thisdischarge end. The central body of the first-mentioned washer, that isthe one not connected to the turbine, is adjusted automatically inresponse to the pressure in the system at the blast furnace thus theannular gap between the body of this washer and its tube is adjusted soas to control the back-pressure of this blast furnace.

In accordance with another feature of this invention the turbine is usedto drive a load, a generator being particularly suitable. In this mannerit is possible to generate electricity with energy that would otherwisebe completely wasted in the system. The turbine according to thisinvention is a so-called expansion turbine wherein a vapor admitted onone side expands in the turbine and drives its rotor.

The invention is based on the surprising fact that it is possible toregulate the pressure at the input end of the system to a very finedegree by controlling only a portion of the gas stream through thesystem. In accordance with the present invention the variable-gap washeris set up for a much higher pressure drop than the other washer that isconnected to the turbine. Thus in accordance with this invention thequantity of air per unit of time passing through the variable Venturiand the other Venturi forms a ratio of between 1:3 and 1:5, i.e. 3 to 5parts by volume per unit time of gas traverses the turbine-feedingVenturi per part of gas traversing the controlled Venturi. This isachieved in accordance with a feature of this invention by providing asingle variable-gap washer and a pair of annular-gap washers connectedto the turbine. In accordance with a further feature of this inventionthe second annular-gap washers connected to the turbine are alsoadjustable for adjustment of the system such that the turbine runs atmaximum efficiency.

Thus in accordance with the present invention the two washers or the twosets of washers can be provided on a single horizontal partition wallprovided in a scrubbing tower. The chamber below the partition wall issubdivided by a further partition into a pair of compartments, one ofwhich is connected to the system output while the other compartment isconnected to the turbine input.

According to yet another feature of this invention a shunt conduit isprovided between the input and output sides of the turbine; valves areprovided at the input and output sides of the turbine and in this shuntconduit so that it is possible to close the valve in the shunt conduitduring normal operation of the turbine and to open this valve in theshunt conduit and close the other two valves to allow servicing and,indeed, removal of the turbine during continued operation of the system.

The two annular-gap washers or sets of washers in accordance with yetanother feature of this invention can be provided one behind the other.The variable-gap wahser is provided downstream of that washer whoseoutput is connected in this case both to the input of the turbine and tothe input of the second washer. According to the present invention thefirst washer is set up so that it can pass 100% of the stack gas whereasthe second one can only pass a maximum of 20% of this gas.

In accordance with the present invention the turbine is so set up thatit has a supplementary gas-cleaning effect that allows the formation ofice crystals in this turbine to be completely avoided. Thus theprescrubber and the first annular-gap washer is operated such that thestack gas is almost completely saturated with water vapor. Thissaturated gas is fed to an expansion turbine that is a one-stage ormultistage centripetal turbine with a centrifugal separator housing andwhose condensation effect is such that the heat of condensationmaintains the fluid state of the condensate. This saturation of thestack gas in no way adversely affects the pressure regulation at thehead of the blast furnace or the like. As long as the level of watervapor in the stack gas approaches the saturation level the heat ofcondensation will ensure that under all operating conditions no icecrystals form. Even though this saturation does decrease slightly theefficiency of the Venturi washers, this slight loss is more thancompensated by the advantage of an additional separating function in theexpansion turbine where the considerable condensation not only preventsice-crystal formation but increases separation of particles from thegas. It is also possible within the scope of this invention to injectwater into the expansion turbine.

The system according to the present invention not only serves to dropthe pressure of and clean stack gases from a blast furnace or the likebut also is able to maintain the pressure of the gas within this furnacesubstantially constant. At the same time the normally wasted energy ofthis stack gas is employed to generate electricity.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a vertical sectional view partly in diagrammatic formillustrating a system according to the present invention;

FIG. 2 is a section taken along line II--II of FIG. 1, drawn to anenlarged scale;

FIG. 3 is a view similar to FIG. 1 illustrating another system inaccordance with this invention;

FIG. 4 is a large-scale view of the detail indicated by arrow IV of FIG.3; and

FIG. 5 is a perspective view partly in section illustrating aturbine-separator according to the present invention.

SPECIFIC DESCRIPTION

As shown in FIGS. 1 and 2 an apparatus for cleaning stack gas comingfrom a blast furnace 1 has a conduit whose extreme upstream section 2aleads from the cupola of the furnace to a coarse-particle separator 3.Another conduit section 2b leads from this particle separator 3 to aprescrubber 4 having a plurality of spray heads 5 that discharge watersprays which, by washing, serve further to remove particles from thestack gas. The thus partially purified gas then passes through a set 6of annular-gap washers from which the gas passes through conduitsections 2c and 2d to a final droplet separator 7 having angled vanes 8.The latter separator 7 removes all of the liquid from the gas before itis pulled away in a clean-gas output conduit 9. The pressure in theconduit section 2a is between 2 and 3 atmospheres and that in conduit 9at the output of the system is approximately 1 atmosphere.

The set 6 of annular-gap washers comprises a plurality of Venturi-typepressure-drop washers 10 and 11 as shown in FIG. 2 having respectivetubes or sleeves 10a, 11a and 11b within each of which is displaceable acentral body 12. Spray heads 13 are provided in the tubes 10a, 11a and11b above the bodies 12 in a manner substantially as described in theabove-cited patents.

The prescrubber 4 and the pressure-drop washer arrangement 6 areprovided in a single upright tower 14 in which the stack gas passes fromtop to bottom. An upwardly concave conical horizontal partition wall 15is provided in the tower 14 with the annular-gap washers 10 and 11passing vertically through this wall 15. Water collected by this wall 15is drawn off through a conduit 16. Thus the wall 15 divides the tower 14into an upper chamber and a lower chamber. An upright partition wall 17divides the chamber below the partition wall into a pair of compartments18 and 19, the single annular-gap washer 10 opening into the compartment18 and the two washers 11 into the compartment 19. The lower ends ofthese compartments are sealed by a single conical wall 20 in which areprovided separate outlet conduits 21 and 22 for carrying off water.

A conduit section 2c is connected to the upper region of the chamber 18and feeds the gas therefrom to the upper end of the droplet separator 7.A similar conduit 24 is connected to the upper end of the chamber 19 andis connected through a valve 28 to the inlet of an expansion turbine 26whose outlet side is connected through a valve 29 to a conduit section2d also connnected to the drop separator 7. A shunt conduit section 27is connected across the two valves 28 and 29 to the opposite sides ofthe turbine 26 and is provided with a shunt-off valve 30 that isnormally closed. Water is drawn out of the droplet separator 7 at anoutlet nipple 31. The valves 28 and 29 can be closed and the valve 30opened to allow servicing and/or removal of the turbine 26 withoutimpairing gas flow through the system according to this invention.

The central body 12 of the annular-gap washer 10 is verticallydisplaceable by a servomotor 23 operated by a controller 39 connected toa sensor 32 at the extreme upstream end of the conduit 2a-2d. When thepressure at the sensor 32 drops below a predetermined level the body 12of the washer 10 is moved downwardly to decrease the annular gap betweenit and the sleeve 10a and thereby increase the back pressure across thiswasher 10. Inversely when the pressure increases above a predeterminedlevel as dictated by the sensor 32 the body 12 is lifted so as todecrease the back pressure across this washer 10 and thereby maintain agenerally constant pressure in the blast furnace 1.

The pressure-drop washers 10 and 11 are so dimensioned that once thefurnace 1 is operating at normal speed approximately four times morestack gas passes through the washers 11 than through the washer 10. Aninstallation as shown in FIG. 1 is used with stack gas at an originalpressure of 15,000 mm water column with 20% of this stack gas passingthrough the washer 10 so as to reduce the pressure by 14,000 mm watercolumn to a pressure of 1,000 mm water column. The remaining 80% of thestack gas is fed through the second washers 11 which reduce the pressureonly by 3,000 mm water column so that the gas is fed to the turbine 26with a pressure 12,000 mm water column. This turbine 26 drops thepressure of 11,000 mm water column so that at the drop separator 7 thegas has a pressure of 1,000 mm water column. Considerable work iscreated by the turbine in this manner.

As the blast furnace 1 is started up the expansion turbine 26 is cut outby closing the valves 28 and 29 and opening the valve 30. Simultaneouslythe washers 10 and 11 are so adjusted that the various separators andscrubbing devices work at maximum efficiency. This can be effected byanother control circuit similar to the control circuit 32. Once theblast furnace 1 is at regular operating condition the control apparatus32 proceeds to function and the washers 11 are set for maximum cleaningefficiency and maximum operating efficiency of the expansion turbine andthe generator 25. The valves 28 and 29 are then opened and the valve 30closed. The control body 12 of the washer 10 is then adjusted so as tomaintain necessary back-pressure at the sensor 32.

In the arrangement shown in FIGS. 3 and 4 the numerals of FIGS. 1 and 2are used wherever the structure is identical. In this arrangement thetower 4' is provided with a pair of series-connected washers 11' and 10'constituting a stepped pressure-drop washer assembly 6'.

The downstream annular-gap washer 10' is provided with a servomotor 33connected to the control 39 so as to allow adjustment of the annular gapin this washer 10', thereby changing the back pressure created thereby.A bypass conduit 35 in which an expension turbine 26 is provided has apair of cutoff valves 36 which allow the turbine 26 to be cut completelyout of the circuit. This bypass conduit 35 opens at its upstream andinto the chamber at the downstream side of the washer 11'. A valve 37 isprovided in the conduit 2c into which the bypass conduit opensdownstream of the turbine 26 at the outlet side of the washer 10'.

The control body 12' of the washer 11' is provided with a servomotor 34connected to a control system (comparator) 38 which pneumaticallydisplaces this control body 2, vertically by means of a cylinderillustrated schematically at 34' in FIG. 4. The upper pressure-dropwasher 11' is capable of passing 100% of the stack gas whereas thedownstream washer 10' can only pass at a maximum 20% of the stack gasflowing through the conduit sections 2a, 2b, 2c. The comparator 38receives a set-point signal S and an actual valve signal A representingthe pressure differential across the upstream differential-pressurewashing device 11'.

The comparator 38 receives a set-point signal S and an actual valuesignal A representing the pressure differential across the upstreamdifferential-pressure washing device 11.

FIG. 5 shows the two-stage expansion turbine 26 according to the presentinvention. This turbine has a centripetal separator housing 41. A gasenters as shown by arrows 42 and leaves as shown by arrows 43. Arrows 44indicate how the centripetal separator housing 41 is shapedsubstantially as a spiral. Condensate with the dust carried therewithleaves the housing 41 at the outlets 45 and 46. With such a turbine 26the prescrubber and the pressure-drop arrangement 11 is set such thatthe gas is virtually saturated with water vapor so that the turbine 26operates with a condensation effect that is so adjusted that the heat ofcondensation maintains the condensate fluid. In addition the expansionturbine 26 can be provided as indicated by arrow 40 with an arrangementfor introducing water to its interior. Thus the expansion in thisturbine 26 functions without formation of ice crystals.

We claim:
 1. A gas-cleaning apparatus for a pressure blast furnacehaving a waste-gas duct connected to said furnace, said apparatuscomprising:a prewasher having a gas inlet and a gas outlet, said inletof said prewasher being connected to and receiving gas from said duct,said prewasher prescrubbing waste gas from said duct; an upstreamdifferential-pressure washer connected to said outlet of said prewasher,said upstream differential-pressure washer comprising a tube member, acontrol member in said tube member defining a variable gap traversed bygas passing through said upstream differential-pressure washer, andcomparator means responsive to the pressure differential across said gapand connected to said control member of said upstreamdifferential-pressure washer for controlling the displacement thereof,said upstream differential-pressure washer having an outlet; adownstream differential-pressure washer connected to the outlet of saidupstream differential-pressure washer and comprising a tubular membertraversed by gas passing through said downstream differential-pressurewasher, a displaceable control member in said tube member of saiddownstream differential-pressure washer and defining a variable gaptherewith traversed by gas, and control means connected to sensor meansin said waste gas duct and responsive to the gas pressure in saidfurnace for shifting said displaceable control member of said downstreamdifferential-pressure washer, said downstream differential-pressurewasher having an outlet; an expansion turbine having a gas inletconnected to the outlet of said upstream differential-pressure washerand an outlet connected to the outlet of said downstreamdifferential-pressure washer; a control valve connected in series withsaid turbine; and a droplet separator connected to the outlet of saidturbine and the outlet of said downstream differential-pressure washer.2. The apparatus defined in claim 1 wherein said comparator meanscomprises means for applying a set-point value signal to said comparatormeans; andmeans for applying an actual-value signal to said comparatormeans representing the pressure differential across the gap of saidupstream differential-pressure washer.
 3. The apparatus defined in claim1 wherein said prewasher includes a tower provided with spray means inan upper portion thereof, the tube member of said upstreamdifferential-pressure washer being disposed below said spray means insaid tower so that gas traversing said upstream differential pressurewasher is substantially completely saturated with water vapor, saidexpansion turbine comprising a centripetal turbine having at least onestage and a centrifugal screening housing.
 4. The apparatus defined inclaim 1, further comprising a coarse-particle separator connectedbetween said duct and said prewasher.
 5. The apparatus defined in claim1 wherein said prewasher and both of said differential-pressure washersare disposed in a common upright column with said prewasher beinddisposed above said upstream differential-pressure washer and saiddownstream differential-pressure washer is disposed below said upstreamwasher.